The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 56 , Issue 660
Showing 1-6 articles out of 6 articles from the selected issue
  • Sadakatu Taneda
    1950 Volume 56 Issue 660 Pages 415-422
    Published: November 15, 1950
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    In his previous paper (this Journal, Vol., LV, No., 646, 1949) the writer concluded that the amount of "magnetite" separated from a magma has an influence on the chemical composition of mafic minerals crystallized from the same magma, but the probable variability in the chemical composition of "magnetite" was not taken into account., In this paper this subject is discussed, based on chemical data of "magnetite" in volcanic rocks (Tables 3, 4 and 5) with the following conclusions : 1) FeO / (Fe 2O 3+TiO 2) in mol proportion of magnetites is comparatively high (up to 1., 4) for basic rocks, whereas almost 1., 0 for acid ones., Fig., 1 shows the variation of Feo, Fe 2O 3 and TiO 2 in the analysed magnetites against SiO 2 percent of the rocks in which they occur., 2) MnO shows no regular variation, and the data for NiO is insufficient in number for general consideration., The amounts of V 2O 3 in the magnetites of basic rocks except for alkaline basalt is higher than those of acid rocks., The M/R ratio (=amount of a certain oxide in magnetite / amount of the same oxide in the mother rock) varies with SiO 2 percent of the rocks, as shown amount of the same oxide in the mother rock) varies with SiO 2 percent of the rocks, as shown in Fig., 2., In acid rocks it varies widely and attains an extremely high value., 3) In basic rocks, the ratio 100/modal "magnetite" is higher than the M/R ratio for TiO 2, MnO and V 2O 3, while in acid rocks the former is smaller than the latter., This fact may show that the amount of modal "magnetite" is overestimated in acid rocks., Notwithstanding this fact, the conclusion in the writer's previous paper needs no revision.,
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  • K. Kinoshita, K. Muta
    1950 Volume 56 Issue 660 Pages 423-432
    Published: November 15, 1950
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    Minor elements in many minerals from epithermal deposits were determined by the spectroscopic method., Distinct variation of the content of minor elements is recognized, correlated with the kind of ore-bringer as well as the kind of ore deposit., The ore from the epithermal deposits, related to Tertiary igneous activity, contains large quantities of low temperature minor elements such as Pb·As·Hg·Ag·Zn, but usually no high temperature elements., There is a systematic variation in the quantities of minor elements, showing a relationship with stage of crystallization or mode of occurrence of minerals, but no relationship with the kinds of wall rocks., It seems obvious that the distribution of minor elements in the minerals depends upon the kind of ore-bringer as well as the physico-chemical conditions under which the mineral-deposition took place.,
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  • Isamu Nakayama
    1950 Volume 56 Issue 660 Pages 433-438
    Published: November 15, 1950
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    Petrographic analysis of the Oboke phyllitic sandstone shows that the quartz crystals are arranged in the manner suggested by the writer's hypothesis which was proposed last year in this journal., From this study, it is ascertained that, as the amount of differential movement in the rocks increases, the quartz crystals undergoes higher degree of rotation, and that several types of petrofabric diagrams of the quartz crystals result from varying amount of the differential movement., Moreover, it is suggested that the types of the petrofabric diagram is determined not only by the amount of the movement but also by the velocity of the movement., The recrystallization of quartz appears to begin at a certain point of each crystal and continue further until the whole crystal is replaced by a new one., This process takes place in the solid state, and the recrystallized quartz grain retains the orientation of the original one.,
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  • Eitaro TAKAHASHI
    1950 Volume 56 Issue 660 Pages 439-440
    Published: November 15, 1950
    Released: April 11, 2008
    JOURNALS FREE ACCESS
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  • Masao Gorai
    1950 Volume 56 Issue 660 Pages 441-443
    Published: November 15, 1950
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    The writer has divided the types of twinning of plagioclase, from a petrological point of view, into C-twin and A-twin (Jour., Geol., Soc., Japan, Vol., 56, No., 655, 1950, p., 149-156)., The present paper describes an easy method of distinguishing them under an ordinary polarisation-microscope without the aid of a universal stage., Under the microscope the twinned plagioclase is distinguished into the following four types (see figure): Type 1-----Polysynthetic twin (1, 2, 4 of the figure) and its modification (3, 5)., Type 2-----Simple twin (6, 7) and its modification (8, 9, 10)., Type 3-----Complex twin and its modification ; this is subdivided into 3a (11-15) and 3b (16-25)., Type 4-----Penetration twin (21-25)., Of these, type 1 is almost always A-twin, and those of types 3 and 4 are always C-twin., However the following three cases are distinguished for the twin of type 2 : 1) The different twin units of a crystal show different retardation when the twinning line is placed in diagonal position with reference to the cross hairs., 2) The twin units show, in that position, equal retardation but show different retardation when a gypsum plate is inserted., 3) The twin units show, in that position, equal retardation even when gypsum plate is inserted., The first two cases are C-twin, but the third case is practically indeterminate.,
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  • [in Japanese]
    1950 Volume 56 Issue 660 Pages 444-444_1
    Published: November 15, 1950
    Released: April 11, 2008
    JOURNALS FREE ACCESS
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